Magnetic storage systems, such as hard disk drives (HDDs), are used as mass storage in a wide variety of devices, including but not limited to personal computers, digital versatile disc (DVD) players, high definition television (HDTV) receivers, vehicle control systems, cellular or mobile telephones, television set top boxes, and portable media players. As these magnetic storage systems become smaller and/or attain higher data storage capacities, the density of data on the magnetic storage medium becomes higher.
A typical HDD includes magnetic storage media of one or more flat disks, called platters (sometimes also “disks” or “discs”). The platters are generally formed of two main substances: a substrate material that gives it structure and rigidity, and a magnetic media coating which holds the magnetic impulses (or moments) that represent data. A typical HDD further includes a read/write head, generally a magnetic transducer which can sense and/or change the magnetic fields stored on the platters. The read/write head is attached to a slider, generally an armature capable of placing the read/write head at a desired location over the platter. The height of the read/write head over the platter is the “fly height.” The fly height of a HDD is a critical distance. If the fly height is too high, the magnetic fields will be too weak or dispersed for the read/write head to function. If the fly height is too low, there is an increased danger of a “head crash,” wherein the read/write head touches the surface of the magnetic storage medium, thereby destroying data and/or damaging the read/write head or the magnetic storage medium.
As the density of data on the magnetic storage medium increases, the strength of the magnetic fields generally decrease, in order to minimize interference. Higher areal density in magnetic storage medium generally requires both advanced read/write transducer design and very fine control of the fly height of the read/write head. Therefore it is desirable to implement closed loop control of the fly height with both fly height actuation and fly height measurement.
One method of sensing fly height is to measure the capacitance between the read/write head and the magnetic storage medium. Capacitance is generally proportional to the distance between two surfaces. As shown in FIG. 1, a read/write head 101 is generally oriented at an angle with respect to the surface 102 of the magnetic storage medium. Therefore the capacitance between the read/write head and the surface of the medium may be determined according to the equation:
                    C        =                              ɛ            0                    ⁢          WL          *                                    ln              ⁡                              [                                                      (                                          d                      +                      s                                        )                                    /                  s                                ]                                      d                                              (        1        )            where C is the capacitance, ε0 is the dielectric constant, W and L are the width and length of the read/write head as shown in FIG. 1, s is the height of the trailing edge of the read/write head, and d is the height of the leading edge of the read/write head over s. FIG. 2 shows a graph of the relationship between the slider-to-disk capacitance and height s of the trailing edge of the read/write head.
Therefore it is desirable to implement a high speed and high resolution method and system for capacitive fly height measurement in the control circuitry of a magnetic storage system.